A number of chemical products have hitherto been used to control vegetative root intrusion in pipeline systems. The most frequently used active ingredients in such products are copper sulfate, corrosive acids or bases, 2,6 dichlorobenzonitrile (hereafter "Dichlobenil") and sodium methyidithiocarbamate (hereafter "Metam"). Each of these products, however, suffer from a number of disadvantages which render their use problematic.
For example, copper sulfate is not detoxified by wastewater treatment plants, where it may either accumulate in the sludge or pass through and contaminate receiving waters. Also, copper sulfate is a systemic herbicide which can damage above-ground vegetation. For these reasons, copper sulfate has fallen into disfavor and its use in many wastewater collection systems is prohibited.
Corrosive acids and bases, such as sulfuric acid, hydrochloric acid, caustic soda, and sulfamic acid, are poured directly into a sewer pipe, where they react with water present in the line to create heat, which burns and kills roots present. Since heat is the primary mechanism of root destruction, these products do little to prevent regrowth and their effectiveness is localized to the point of application. To address some of these problems, certain formulations of corrosives contain copper sulfate or Dichlobenil as additional active ingredients.
Dichlobenil is a common herbicide that acts upon growth points in root systems and therefore provides residual control by deterring regrowth. Because its effectiveness is limited, Dichlobenil is commonly formulated with the active agent Metam.
Metam, and its primary breakdown product MITC, exert their herbicidal action by rupturing plant cell membranes. It has a broad scope of uses, as it is a non-systemic and non-selective herbicide. Metam is a very volatile compound, producing a gas (MITC) when mixed with water; the gas has pesticidal properties and penetrates root growths. It is easy to use in that it is highly soluble in water and is compatible with most foaming agents used for application. Combinations of Metam and Dichlobenil have been found to be so effective, they have virtually replaced other types of active ingredients in the industry. However, several problems associated with Metam have developed which create a motivation to find other suitable herbicides for root control. First, the volatility and toxicity of Metam pose a threat to worker safety. Second, in concentrations typically used for root control, Metam may be toxic to microorganisms at biological wastewater treatment plants, where it may be particularly toxic to nitrifying bacteria. Third, Metam is a marine pollutant, and therefore is not amenable to storm drain applications unless costly precautions are taken to ensure against a release of Metam into fresh water sources such as streams, ponds and lakes.
In contrast to the foregoing agents, the herbicide Diquat has not been contemplated for use in root control. Diquat's primary mode of action is to destroy plant tissue by impairing photosynthesis in the green parts of plants, and is therefore operant on plant tissues that are exposed to light. This mode of action would suggest that Diquat may not damage the roots themselves, but rather enter the plant through the roots and destroy the upper parts of the plant, an undesirable effect. Moreover, the Diquat cation which is responsible for herbicidal action becomes tightly bound to organic substances, upon which it is rendered inactive. In view of the high concentrations of organic substances in soil and sewer pipes, one would have expected that Diquat would be rapidly inactivated and therefore would not be a viable candidate for use in sewers.